Internal combustion engines commonly employ hydraulic lifters (also called followers or tappets) within their valve trains. The hydraulic lifters are intended to reduce or eliminate lash within the valve trains. That is, the hydraulic lifters adjust in their length to compensate for small amounts of space that can arise between the valves of the engine and their valve seats (on the cylinder heads) due to changes in the operating temperature of the engine and other factors. Without compensating for this lash, the valve trains can result in early, late or otherwise improper opening and closing of the valves.
Referring to FIG. 1 (Prior Art), a flow diagram schematically shows how, in one exemplary embodiment, oil or other lubricant is pumped in an engine from an oil pump 10 to four hydraulic lifters 12,14,16 and 18. Specifically, oil is provided from the oil pump 10 to an oil filter 20, at which the oil is filtered. The oil then is provided both to a flywheel (FW) bearing 22 and (in this embodiment) also to a power takeoff (PTO) bearing 24. From the FW bearing 22, oil is then directed to a camshaft bearing 26, and then to a lifter feed gallery 28. The lifter feed gallery 28 in turn is capable of providing the oil simultaneously to all of the four hydraulic lifters 12,14,16 and 18. In the present embodiment, the hydraulic lifters 12 and 14 form a pair of lifters, with the former hydraulic lifter being an intake lifter and the latter being an exhaust lifter. Similarly, the hydraulic lifters 16 and 18 form a pair, with the former being an intake lifter and the latter being an exhaust lifter.
Referring to FIG. 2 (Prior Art), a valve train 30 employing the hydraulic lifters 12,14 is shown in detail. As shown, a gear 32 is rotated by a crankshaft (not shown) within the engine crankcase (also not shown), and causes cams 34,36,38 and 40 to rotate. The cams 34,36,38 and 40 are positioned within the engine crankcase. Bottom sides 42,44 of the hydraulic lifters 12,14 rest upon two of the cams 36 and 40, respectively, while push rods 46,48 in turn rest upon top sides 52,54 of the hydraulic lifters, respectively. The opposite ends of the push rods 46,48 in turn interface respective rocker arms 56,58, the opposite sides of which interface valves 62,64. Springs 50,60 between the respective rocker arms 56,58 and the crankcase (not shown) tend to maintain the valves 62,64 in closed positions and tend to force the push rods 46,48 and hydraulic lifters 12,14 toward the cams 36,40. The valves 62,64 are opened when large lobes 66 of the cams 36,40 encounter the hydraulic lifters 12,14.
The hydraulic lifters 12,14 themselves rest within cavities within the engine. When oil is provided to those cavities, oil collects within oil grooves 72, 74 along the sides of the respective hydraulic lifters 12,14, and further enters into the hydraulic lifters by way of oil holes 76,78 located within the respective oil grooves. Operation of the hydraulic lifters 12,14 including the oil to eliminate lash occurring in the valve train is well known to ordinary persons skilled in the art.
Turning to FIG. 3 (Prior Art), a conventional lifter feed gallery 28 is configured for operation in conjunction with valve trains of the type discussed above, that is, in which cams are situated within the engine crankcase and their movement controls the opening and closing of valves by way of hydraulic lifters, push rods and rocker arms. As shown, the lifter feed gallery 28 includes oil 70 that flows into the lifter feed gallery from the camshaft bearing 26 by way of an oil feed passage 80. The oil 70 in turn flows through the lifter feed gallery 28 into four lifter feed holes 82,84,86 and 88 and then flows, by way of those holes, to the four hydraulic lifters 12,14,16 and 18. (The direction of flow of oil into and out of the lifter feed gallery 28 by the oil feed passage 80 and the lifter feed holes 82,84,86 and 88 is indicated by dots indicating inward flow and crosses indicating outward flow.)
As shown, when positioned on an engine for normal operation, the lifter feed gallery 28 is essentially an inverted U-shaped channel, in which the bottom of the U is directed upward, and the oil feed passage 80 is located at the top of the lifter feed gallery. Also as shown, when the lifter feed gallery 28 is in its normal orientation (e.g., the engine is not tipped), one of the lifter feed holes 82 of the lifter feed gallery is located slightly above the oil feed passage 80, while the remaining lifter feed holes 84,86 and 88 are all located below the oil feed passage.
The lifter feed gallery 28 is specifically designed for engines that employ valve trains of the type shown FIG. 2, in which the hydraulic lifters 12,14,16 and 18 are located proximate the engine crankcase and proximate one another, rather than proximate the different valve seats of the different engine cylinders. It is in this type of engine that a single lifter feed gallery 28 can provide the oil 70 to multiple hydraulic lifters 12,14,16 and 18 by way of the short lifter feed holes 82,84,86 and 88.
Although the hydraulic lifters 12,14,16 and 18 often operate well in preventing or diminishing lash within the valve trains of the engine, this is not always the case. Sometimes, the hydraulic lifters fail to sufficiently reduce lash and produce lifter noise or chatter. The lifter noise particularly occurs when the valves close at points in the profiles of the cams 34,36,38 and 40 where the seating velocities are quite high. Utility engines having relatively high operating temperatures (and fuel dilution), as well as vertical crankshaft engines having hydraulic lifters that are oriented in a relatively horizontal manner within the valve trains of the engine, are particularly susceptible to this lifter noise. Also, lifter noise can be exacerbated within utility engines that are employed in machinery such as lawnmowers, which are often operated at angles that are significantly off of the horizontal and experience significant jostling as the machinery moves about.
It would therefore be advantageous if an improved oil feed system for hydraulic lifters could be designed that eliminated or reduce lifter noise and improved lifter performance. It would further be advantageous if such an improved oil feed system could be implemented in engines having valve trains as described above. In particular, it would be advantageous if such an improved oil feed system required only minor modifications from existing oil feed systems and therefore could be simply and cost-effectively manufactured.